Gear pump

ABSTRACT

Gear pump (1) for pumping liquids, of the type comprising: a stator unit (2), which is equipped with a substantially cylindrical cavity (3) and is designed to generate a magnetic field rotating on the inside of said cavity (3); a substantially tubular, cylindrical bush (4), which is keyed on the inside of the cavity (3) of the stator unit (2); and at least one pumping gear (5, 6) housed in an axially rotatable manner on the inside of the bush (4); one or more longitudinal grooves (12) being present in the zone of contact between the stator unit (2) and the bush (4), said longitudinal grooves extending in the interstitial space between the bush (4) and the stator unit (2) and being designed to conduct an adhesive inside the interstitial space between the bush (4) and the stator unit (2).

BACKGROUND OF THE INVENTION

The present invention relates to a gear pump for pumping liquids.

More specifically, the present invention relates to an electrically operated gear pump which can advantageously be used to feed fuel to an internal combustion engine. This is a use to which the text which follows will make explicit reference, without thereby losing generality.

As is known, a number of models of electrically operated gear pumps for liquids comprise: an annular stator unit capable of generating a rotating magnetic field; a ring gear with inner toothing, which is inserted/fitted in an axially rotatable manner on the inside of the stator unit; and finally a gear wheel, which is fitted in an axially rotatable manner on a support pin positioned eccentrically on the inside of the ring gear and meshes on the inner toothing of the ring gear.

The rotation of the ring gear on the inside of the stator unit creates a movable volume that is capable of transferring a predetermined quantity of fuel or other liquid from the intake port of the pump to the delivery port of said pump. The flow of the liquid exiting the pump obviously depends on the speed of rotation of the ring gear.

In some cases, the gear pump is finally also equipped with a tubular bush, which is interposed between the outer surface of the ring gear and the inner surface of the stator unit in such a way as to reduce the wear of the two components and at the same time facilitate the insertion of the two gears into the stator unit.

Unfortunately, the assembly of the bush on the inside of the stator unit is a relatively complicated and expensive process.

Specifically, the tubular bush is generally fixed immovably on the inside of the stator unit by means of the adhesive which is injected into the interstitial space between the bush and the stator unit. Unfortunately, however, the mechanical play present between the bush and the stator unit is reduced to such an extent as to make it extremely difficult for the adhesive to penetrate between the two components, and therefore the adhesive is injected into the interstitial space between the bush and the stator unit by means of particularly complicated and expensive machinery.

SUMMARY OF THE INVENTION

It is an object of the present invention to simplify and speed up the assembly of the gear pumps described above.

Moreover, the present invention also provides a method for assembling a gear pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting exemplary embodiment thereof and in which:

FIG. 1 is a sectional view of a gear pump formed according to the requirements of the present invention; whereas

FIG. 2 is a partially exploded perspective view of the gear pump shown in FIG. 1, with parts removed for clarity.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, the numeral 1 denotes, in its entirety, an electrically operated gear pump for pumping liquids, which can advantageously be used to feed fuel to an internal combustion engine.

The gear pump 1 comprises essentially: a stator unit 2, which is equipped internally with a substantially cylindrical cavity 3 and is structured in such a way as to be able to generate a magnetic field rotating on the inside of the cavity 3; a substantially tubular, cylindrical bush 4, which is keyed/inserted on the inside of the cavity 3 immovably and preferably also in such a way as to rest substantially uniformly on the inner surface of the stator unit 2; and at least one pumping gear housed in an axially rotatable manner on the inside of the bush.

More specifically, the gear pump 1 is preferably equipped with a pair of pumping gears 5 and 6, which are housed in an axially rotatable manner on the inside of the tubular bush 4 and at the same time mesh into one another.

The bush 4, on the other hand, is preferably formed by a tubular cylindrical body preferably made of a plastic material. The thickness of the tubular body 4 is preferably furthermore between 0.1 and 3 mm (millimetres).

With reference to FIGS. 1 and 2, the stator unit 2, on the other hand, comprises a plurality of polar cores 8, which are preferably made of a magnetic material, are evenly spaced angularly about the longitudinal axis A of the cavity 3, and are equipped with polar heads 9, which face the cavity 3 and contribute to delimiting/defining the perimeter of the cavity 3; and the outer surface of the tubular bush 4 rests directly on the polar heads 9 of the various polar cores 8.

In the example shown, in particular, each polar core 8 is preferably formed by a stack of laminations, which are placed closely next to one another and are preferably made of a ferromagnetic material.

It is preferable that the stator unit 2 further also comprises a preferably substantially cylindrical outer tubular jacket 10, which is preferably made of a metallic material and extends coaxially with the longitudinal axis A in such a way as to surround the polar cores 8 of the stator unit 2 and the bush 4.

It is preferable that each polar core 8 further forms a link and/or extends in a cantilevered manner from the tubular jacket 10 towards the bush 4 positioned in the centre of said tubular jacket 10.

More specifically, in the example shown, the tubular jacket 10 is also preferably formed by a stack of laminations, which are placed closely next to one another and are preferably made of a ferromagnetic material, and the polar cores 8 are preferably formed in one piece with the tubular jacket 10.

In other words, the metallic laminations which form the outer tubular jacket 10 are cut in such a way as to also form the polar cores 8.

With reference to FIG. 1, the stator unit 2 further also comprises a series of induction coils 11, which are wound around the various polar cores 8 in such a way as to be able to generate, when electric current passes through them, a radial magnetic field on the inside of the cavity 3. By energizing the induction coils 11 of the stator unit 2 in a known manner, it is possible to generate, on the inside of the cavity 3 and of the tubular bush 4, a radial magnetic field which rotates about the longitudinal axis A of the cavity 3 and is capable of driving at least one of the pumping gears 5 and 6 to rotate.

With reference to FIGS. 1 and 2, the zone of contact between the tubular bush 4 and the stator unit 2, or more precisely between the tubular bush 4 and at least one of the polar heads 9 of the stator unit 2, moreover also has one or more longitudinal grooves 12, which extend in the interstitial space between the tubular bush 4 and the stator unit 2, preferably substantially over the entire axial length t of said zone of contact, and are dimensioned in such a way as to conduct/allow the flow of the liquid adhesive needed to permanently fix the tubular bush 4 to the stator unit 2 inside the interstitial space between the tubular bush 4 and the stator unit 2.

The groove or grooves for supplying the adhesive 12 is or are preferably also substantially rectilinear and/or locally parallel with one another, and optionally also parallel to the longitudinal axis A of the cavity 3 and of the bush 4.

More specifically, the zone of contact between the tubular bush 4 and the stator unit 2, or more precisely between the tubular bush 4 and at least one of the polar heads 9 of the stator unit 2, is preferably provided with a plurality of grooves for supplying the adhesive 12 which are arranged one alongside another.

With reference to FIGS. 1 and 2, in the example shown, in particular, the groove or grooves for supplying the adhesive 12 is or are preferably formed directly on the polar head 9.

More specifically, the groove or grooves for supplying the adhesive 12 extends or extend along the cylindrical surface of the polar head 9, preferably remaining parallel to the longitudinal axis A and preferably over the entire axial length t of the polar head 9.

In other words, the groove or grooves for supplying the adhesive 12 is or are preferably formed by appropriately cutting/severing the laminations which contribute to forming the polar core 8.

More specifically, with reference to FIGS. 1 and 2, in the example shown, each one of the polar heads 9 of the stator unit 2 is preferably equipped with a plurality of grooves for supplying the adhesive 12, which extend on the cylindrical surface of the polar head 9 one alongside another, over the entire axial length f of the polar head 9, and are dimensioned in such a way as to conduct/allow the flow of the adhesive needed to permanently fix the tubular bush 4 to the stator unit 2 rapidly inside the interstitial space between the tubular bush 4 and the stator unit 2.

It is preferable that the grooves for supplying the adhesive 12 are also spaced apart in a substantially uniform manner along the entire width of the polar head 9.

With reference to FIG. 1, it is preferable for the pair of pumping gears, on the other hand, to comprise: a circular ring gear 5, which has the toothing on its inside, i.e. facing towards the centre, and is housed in an axially rotatable manner on the inside of the bush 4, coaxially with the longitudinal axis A of the cavity 3 and of the bush 4; and a gear wheel 6, which is fitted in an axially rotatable manner on a support pin 13 positioned eccentrically on the inside of the ring gear 5 and meshes on the inner toothing of the ring gear 5.

The ring gear 5 is preferably made of a plastic material or of a sintered metallic material and preferably internally incorporates a series of permanent magnets (not shown), which interact with the rotating magnetic field generated by the stator unit 2, producing a torque which drives the ring gear 5 to rotate about the longitudinal axis A.

In a different embodiment, however, instead of the permanent magnets, the ring gear 5 may have a series of cavities, which locally attenuate the magnetic flux and interact with the rotating magnetic field generated by the stator unit 2, producing a torque which drives the ring gear 5 to rotate about the longitudinal axis A.

As an alternative, the ring gear 5 may also internally incorporate a series of elements made of an electrically conductive material which are arranged in such a way as to form a squirrel cage.

Similarly to the ring gear 5, the gear wheel 6 is also preferably made of a plastic material or of a sintered metallic material.

With reference to FIG. 1, it is preferable that the gear pump 1 is finally provided with an outer casing 14, which is equipped on the inside with a structured/shaped cavity for accommodating the stator unit 2, the tubular bush 4 and the two pumping gears 5 and 6 and at the same time closing the two axial ends of the cavity 3, preferably in a fluid-tight manner

The support pin 13 of the gear wheel 6 is preferably furthermore fixed firmly on the outer casing 14.

More specifically, in the example shown, the outer casing 14 preferably comprises: a substantially cylindrical cup-shaped body 15, which is dimensioned so as to be able to accommodate, resting on the bottom thereof, the stator unit 2, the tubular bush 4 and the two pumping gears 5 and 6; and a disc-shaped cover (not shown) positioned so as to close the opening of the cup-shaped body 15, in such a way as to plug the second axial end of the cavity 3. The support pin 13 preferably further extends in a cantilevered manner from the bottom of the cup-shaped body 15, and is preferably formed in one piece with the latter.

The operation of the gear pump 1 can easily be inferred from that described above and does not need to be explained further.

The method for mounting the gear pump 1 provides for inserting the tubular bush 4 into the cavity 3 of the stator unit 2, and then injecting directly into the longitudinal grooves 12 the adhesive needed to immovably fix/block the tubular bush 4 on the polar heads 9 of the stator unit 2.

Preferably, but not necessarily, the method for assembling the gear pump 1 moreover provides for inserting at least one of the two pumping gears 5, 6 into the bush 4, before inserting the bush 4 into the cavity 3 of the stator unit 2.

More specifically, the method for assembling the gear pump 1 preferably provides for inserting at least the ring gear 5 into the bush 4, before inserting the bush 4 into the cavity 3 of the stator unit 2.

The presence of the longitudinal grooves 12 offers a number of advantages.

Firstly, the longitudinal grooves 12 make it possible to inject the adhesive more quickly into the interstitial space between the tubular bush 4 and the stator unit 2, speeding up the production process.

Moreover, the longitudinal grooves 12 make it possible to distribute the adhesive with greater homogeneity in the interstitial space between the tubular bush 4 and the stator unit 2, with all the advantages this involves.

It is lastly clear that modifications and variants can be brought about with respect to the gear pump 1 without thereby departing from the scope of the present invention.

By way of example, the tubular bush 4 could be made of bronze and/or the groove or grooves for supplying the adhesive 12 could extend on the cylindrical surface of the polar head 9, following a preferably substantially helical curved trajectory. 

1. A gear pump (1) for pumping liquids, the gear pump comprising: a stator unit (2), which defines a substantially cylindrical cavity (3) and which is cnfigured to generate a magnetic field rotating on an inside of said cavity (3); a substantially tubular, cylindrical bush (4), which is keyed on the inside of the cavity (3) of the stator unit (2); at least one pumping gear (5, 6) housed in an axially rotatable manner on an inside of the bush (4); and one or more longitudinal grooves (12) in a zone of contact between the stator unit (2) and the bush (4), said one or more longitudinal grooves extending in an interstitial space between the bush (4) and the stator unit (2) and being configured to conduct an adhesive inside the interstitial space between the bush (4) and the stator unit (2).
 2. The gear pump according to claim 1, wherein (1) the longitudinal groove or grooves (12) extends or extend on an inside of the interstitial space between the bush (4) and the stator unit (2), substantially over an entire axial length (l) of the zone of contact.
 3. The gear pump according to claim 1, wherein the longitudinal groove or grooves (12) is or are substantially rectilinear.
 4. The gear pump according to claim 1, wherein the longitudinal groove or grooves (12) follows or follow a substantially helical curved trajectory.
 5. The gear pump according to claim 1, wherein the zone of contact between the stator unit (2) and the bush (4) is provided with a plurality of longitudinal grooves (12) alongside one another.
 6. The gear pump according to claim 1, wherein the stator unit (2) comprises a plurality of polar cores (8), which surround said cavity (3) and are equipped with polar heads (9) which contribute to delimiting/defining the perimeter of said cavity (3); the longitudinal groove or grooves (12) being formed on at least one of said polar heads (9).
 7. The gear pump according to claim 1, wherein the bush (4) is a cylindrical tubular body made of a plastic material.
 8. The gear pump according to claim 1, wherein said at least one pumping gear (5, 6) comprises: a ring gear (5) with inner toothing, is the ring gear being housed in an axially rotatable manner on the inside of the bush (4); and a gear wheel (6), which is fitted in an axially rotatable manner on a support pin (13) positioned eccentrically on an inside of the ring gear (5) and meshes on the inner toothing of the ring gear (5).
 9. A method for assembling a gear pump (1) for pumping liquids, the gear pump comprising: a stator unit (2), which defines a substantially cylindrical cavity (3) and is configured to generate a magnetic field rotating on an inside of said cavity (3); a substantially tubular, cylindrical bush (4), which is keyed on the inside of the cavity (3) of the stator unit (2); and at least one pumping gear (5, 6) housed in an axially rotatable manner on an inside of the bush (4); the method comprising the steps of inserting the bush (4) into the cavity (3) of the stator unit (2), and then injecting an adhesive into one or more longitudinal grooves (12) extending in an interstitial space between the bush (4) and the stator unit (2).
 10. The method for assembling a gear pump according to claim 9, wherein the method further comprises the step of inserting said at least one pumping gear (5, 6) into the inside of the bush (4), before inserting the bush (4) into the cavity (3) of the stator unit (2).
 11. A gear pump (1) for pumping liquids, the gear pump comprising: a stator unit (2), which defines a substantially cylindrical cavity (3) and which is configured to generate a magnetic field rotating on an inside of said cavity (3); a substantially tubular, cylindrical bush (4), which is keyed on the inside of the cavity (3) of the stator unit (2); at least one pumping gear (5, 6) housed in an axially rotatable manner on an inside of the bush (4); and one or more longitudinal grooves (12) in a zone of contact between the stator unit (2) and the bush (4), said one or more longitudinal grooves extending in an interstitial space between the bush (4) and the stator unit (2) and containing an adhesive fixing the bush to the stator unit.
 12. The gear pump according to claim 11, wherein (1) the longitudinal groove or grooves (12) extends or extend on an inside of the interstitial space between the bush (4) and the stator unit (2), substantially over an entire axial length (l) of the zone of contact.
 13. The gear pump according to claim 11, wherein the longitudinal groove or grooves (12) is or are substantially rectilinear.
 14. The gear pump according to claim 11, wherein the longitudinal groove or grooves (12) follows or follow a substantially helical curved trajectory.
 15. The gear pump according to claim 11, wherein the zone of contact between the stator unit (2) and the bush (4) is provided with a plurality of longitudinal grooves (12) alongside one another.
 16. The gear pump according to claim 11, wherein the stator unit (2) comprises a plurality of polar cores (8), which surround said cavity (3) and are equipped with polar heads (9) which contribute to delimiting/defining the perimeter of said cavity (3); the longitudinal groove or grooves (12) being formed on at least one of said polar heads (9).
 17. The gear pump according to claim 11, wherein the bush (4) is a cylindrical tubular body made of a plastic material.
 18. The gear pump according to claim 11, wherein said at least one pumping gear (5, 6) comprises: a ring gear (5) with inner toothing, is the ring gear being housed in an axially rotatable manner on the inside of the bush (4); and a gear wheel (6), which is fitted in an axially rotatable manner on a support pin (13) positioned eccentrically on an inside of the ring gear (5) and meshes on the inner toothing of the ring gear (5). 